With the presidential campaign dominating the airwaves, social media feeds, and dinner table conversations across America, it’s easy to forget that there’s another equally important election taking place this November: the race for control of Congress.

You can be sure that the United States Chamber of Commerce has not forgotten. On Wednesday, the Chamber’s chief political strategist told the Washington Post “We think early money sets the terms of the debate, and we’re gearing up” in reference to the Chamber’s plans to spend heavily on Senate races. The Chamber has already been showering hundreds of thousands of dollars on several Republican senate candidates. Mark Kirk (R-IL) and Pete Toomey (R-PA) have each benefited from over $500,000 in Chamber spending. And Rob Portman (R-OH) has benefited as the Chamber has spent more than $500,000 against his opponent, Ted Strickland (D-OH). Joe Heck, Republican candidate for Senate in Nevada has benefited from over $400,000 in Chamber spending while Senators John McCain (R-AZ) and Kelly Ayotte (R-NH) have seen the Chamber spend over $350,000 each to promote their reelection bids. Previous reports indicate that the Chamber may shell out a total of $100 million on elections spending in 2016.

With the first quarter of 2016 drawing to a close, Public Citizen’s Chamber Watch decided to look and see how much the Chamber had spent on election campaigns so far this year, and how it stacked up compared to other outside spending groups. Thus far, the Chamber has spent almost $3.7 million. That places it in twelfth place on the list of largest outside spenders, made up largely of Super PACs and 504(c)(4) organizations. These organizations may accept unlimited donations, but are technically not allowed to coordinate with the official campaigns of the candidates they support. However, the list is dominated by groups supporting or opposing specific presidential candidates, and if you remove these groups focused on the Presidential election, the Chamber rises to first place on the list.

The Chamber also stands out in that it is by far the largest outside spender that does not disclose any of its donors. In other words, the Chamber’s election spending is 100% secret money. Indeed, of the top 25 outside spenders, only one other group, the Koch brothers-affiliated and Orwellian-named Americans for Prosperity, does not disclose any of its donors.

When we take a look at the money going out the doors in term of the Chamber’s election spending (since we can’t look at what is coming in), it reveals a hyper partisanship, in contrast to claims to the contrary. Thus far this year, the Chamber has spent $2.9 million in support of Republican candidates, more than $500,000 against Democratic candidates, and precisely $0 in favor of Democratic candidates or against Republican candidates.

Such lopsided spending might surprise the millions of businesspeople who don’t see public policy in starkly partisan terms. But it shouldn’t come as a surprise to those who’ve studied the Chamber under its current president, Tom Donohue. Donohue has turned what was once a non-partisan organization into a fiercely partisan lobbying, litigation, and elections spending behemoth. While the Chamber might claim to represent the interests of all American businesses and indeed the American economy as a whole, the reality is that the Chamber is essentially a hired gun, lobbying for the interests of its biggest contributors. That’s likely one of the reasons why the Chamber has consistently opposed legislative and regulatory efforts to combat climate change. And that’s probably why the Chamber has fought tooth and nail against the passage and implementation of the Dodd-Frank Wall Street Reform Act, even after the financial crisis exposed the need for the reforms included in it.

The 2016 congressional races are just starting to heat up, and the vast majority of election spending for these races will come in the fall. The flow of undisclosed money through the Chamber is therefore likely to accelerate. While Washington’s heaviest downpours usually take place during summer thunderstorms, this year, as in past election years, the Chamber is likely to let loose torrents of secret money to elect its favorite senators and congresspeople this fall. The Chamber of Commerce weather forecast for Capitol Hill can be summed up in three words: make it rain.